Designed and manufactured in the UK, Viking present their precision engineered ring adapter. This ring adapter fits securely onto the Viking Universal Smartphone Digiscoping Adapter and allows the device to be snugly connected to telescopes/spotting scopes with an eyepiece diameter of 56mm.
You can work out your scope's eyepiece size by either measuring its diameter, check the specification printed on the side or in the instruction guide that came with. This ring size is known to fit the following popular spotting scopes -
RSPB 82HD Telescope 25-50x
Nikon DS Eyepieces 20-60x